Gallium–Arsenide-Based Bipolar Cascade Lasers With Deep Quantum-Well Tunnel Junctions

Edge-emitting GaAs-based lasers were fabricated from metal-organic chemical vapor deposition-grown material containing two diode laser structures separated by a quantum-well tunnel junction (QWTJ). The QWTJ was comprised of a thin, high indium content InGaAs layer sandwiched between relatively low-doped p-type and n-type GaAs layers. Comparison of near-field data with predictions from a one-dimensional current spreading model and comparison of current-voltage characteristics for these two-stage or double-stage lasers (DSLs) with single-stage lasers (SSLs) shows that this type of reverse-biased QWTJ has a low effective resistivity. As a consequence, current spreading perpendicular to the laser length in the plane of the layers (lateral direction) is reduced leading to a relatively low threshold current density for the second stage. In addition, the differential quantum efficiency of these DSLs is nearly twice that of SSLs